Pin fin compliant heat sink with enhanced flexibility

ABSTRACT

Heat sinks and methods of using the same include a top and bottom plate, at least one of which has a plurality of pin contacts flexibly connected to one another, where the plurality of pin contacts have vertical and lateral flexibility with respect to one another; and pin slice layers, each having multiple pin slices, arranged vertically between the top and bottom plates such that the plurality of pin slices form substantially vertical pins connecting the top and bottom plates.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under Contract No.:DE-EE0002894 (Department of Energy (DOE)). The Government has certainrights to this invention.

BACKGROUND

Technical Field

The present invention relates to cooling and, more particularly, to pinfin compliant heat sinks having enhanced flexibility.

Description of the Related Art

Compliant heat sinks provide a good heat removal solution with lowthermal resistance and substantially lower thermal interface stressesthan standard, rigid heat sinks. Compliant heatsinks are able to conformto an irregular device surface without damage to the heatsink or to thedevice. In particular, pin fin compliant (PFC) and linked pin fincompliant (LPFC) heat sinks have favorable compliant performance at arelatively low cost.

PFC heat sinks include an array of pins between two compliant membranes.The PFC assembly is forced into contact with a device to be cooled usinga compression layer. Small, local deviations from flatness are handledby PFCs with relatively low loads, as neighboring pins can move up anddown relative to one another. Global deviations (such as a curvedsurface) can also be handled with sufficient loading, but the load needsto be high enough to bend the PFC heat sink as a whole. This puts one ofthe membranes in tension, resisting the bending. In the case of LPFCheat sinks, the links between individual pins also tend to resistbending. As such, standard PFC and LPFC heat sinks use high degrees ofloading force when used on curved surfaces. These high loads create arisk of damage when installing or removing the heatsink, whether to theheatsink itself or to the device to be cooled.

SUMMARY

A heat sink includes a top and bottom plate, at least one of whichincludes a plurality of pin contacts flexibly connected to one another.The plurality of pin contacts have vertical and lateral flexibility withrespect to one another. The cooling device further includes verticalpins connecting the top and bottom plates.

A linked pin fin compliant heat sink includes a top and a bottom plate.A plurality of pin slice layers, each comprising a plurality of pinslices, is arranged vertically between the top and bottom plates suchthat the plurality of pin slices form substantially vertical pinsconnecting the top and bottom plates. There is a plurality of curvedlinks connecting laterally adjacent pin slices in at least a pin layer.

A method for employing a heat sink includes placing a pin fin compliantheat sink on a non-flat surface. The pin fin complaint heat sink has topand bottom plates connected by a plurality of pins arranged verticallybetween the top and bottom plates. The top and bottom plates arevertically conformed to local deviations of the non-flat surface. Thetop and bottom plates are laterally conformed to an overall shape of thesurface, wherein at least either the top or bottom plate is corrugated.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The disclosure will provide details in the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1 is a cross-sectional view of a pin fin compliant heat sink inaccordance with the present principles;

FIG. 2 is a cross-sectional view of a linked pin fin compliant heat sinkin accordance with the present principles;

FIG. 3 is a top-down view of a layer of pin slices and linkstherebetween in accordance with the present principles;

FIG. 4 is a three-dimensional view of the top of a corrugated plate inaccordance with the present principles;

FIG. 5 is a three-dimensional view of the bottom of a corrugated platein accordance with the present principles;

FIG. 6 is a block/flow diagram of a method of using a pin fin compliantheat sink in accordance with the present principles;

FIG. 7 is a cross-sectional view of a linked pin fin compliant heat sinkon a globally curved surface in accordance with the present principles;and

FIG. 8 is a cross-sectional view of a linked pin fin compliant heat sinkin on an irregular surface accordance with the present principles.

DETAILED DESCRIPTION

Embodiments of the present invention provide pin fin compliant (PFC) andlinked pin fin compliant (LPFC) heat sinks with enhanced flexibilitythat allow the heat sinks to be used on curved surfaces withsubstantially lower loads than those needed by conventional heat sinks.To accomplish this, the present embodiments employ pin membranes(plates) that are corrugated between pin contacts, which greatly reducesthe effective modulus of the membrane in tension or compression,allowing the plates to accommodate lateral displacements as well asvertical displacements. Lateral displacement along the top plate allowsthe pins to angle away from one another, such that an overall curvedsurface may be accommodated. Thus, the present embodiments providecooling solutions for devices and surfaces having irregularconfigurations, greatly expanding the options for using such devices innew environments.

In the context of LPFC heat sinks, the links between the pins shown inthe present embodiments may have a curved shape, rather than a straightone. This curved shape will also have a lower modulus in compression ortension than a straight, centered link, allowing for much more lateralcompression than straight links would have. The curved links in the LPFCheat sink of the present embodiments can also be formed at a higherdensity in areas where lower flow is desired, while still maintainingflexibility. This reduces or eliminates the need for separate flowblocking elements, as the heat sink itself can be constructed to providespecific flow pathways.

Referring now to the drawings in which like numerals represent the sameor similar elements and initially to FIG. 1, an exemplary embodiment ofa PFC cooling device is shown. A chip 104 is mounted on a substrate 102.For the present purposes, the chip 104 may be any appropriate device orcircuit, and it is specifically contemplated that the chip 104 will bean integrated circuit package, mounted on a printed circuit boardsubstrate 102. Although the chip 104 is shown as being flat for ease ofillustration, it should be recognized that the top surface of the chip104 may be uneven or curved. It is assumed for the present purposes thatthe chip 104 generates heat during operation, which necessitates someform of cooling, though the heat could also be generated within orbehind the substrate 102.

A cooling device 106 is mounted on the chip 104, either directly or withsome appropriate thermally conductive medium such as a thermal paste.The chip 104 has some irregularity in its surface, including one or moreof local irregularities, such as a feature that extends from the planeof the surface. The chip 104 may also include global irregularities,such as an overall curve. According to the present principles, thecooling device 106 conforms to the surface of the chip 104 when pressureis applied. Heat passes to the cooling device 106 from the chip 104 andis dissipated by pins/fins 108. In the present example, the coolingdevice is an enclosure that channels air or some other coolant past pins108, transporting the dissipated heat away from the chip 104. Thecoolant in question may be any appropriate fluid having suitablemechanical and thermal properties, including a high heat capacity and alow viscosity. In one specific embodiment, it is contemplated that watermay be used as a coolant, but alternative coolants such as air, oil, ora liquid metal such as mercury, gallium or a gallium alloy such as withtin or indium.

A load 112 is applied to the cooling device 106. The load 112 isspecifically contemplated as being a force provided by, e.g., a clamp,weight, or some other device that holds the cooling device 106 tightlyonto the chip 104. The pressure generated by the load 112 provides goodthermal contact between the cooling device 106 and the chip 104. Athermal paste or other thermally conductive compound (not shown) may beinterposed between the cooling device 106 and the chip 104 to maximizethermal contact and heat flow between the two.

As noted above, the chip's surface may be uneven or curved. Byconforming to the uneven surface of the chip 104, the cooling device 106will have some corresponding deformation on its top surface as the pins108 translate the deformation from the chip's surface. As such, anelastomer or spring array 110 is used between the load 112 and thecooling device 106 to transfer the force of the load 112 evenly acrossthe cooling device 106. The elastomer 110 can be, for example, a rubbersheet which is disposed between the surface of load 112 and the top lidof the heat sink 106. The elastomer 110 may alternatively be formed asthe top lid of the heat sink 106 itself, though care should be taken toensure that coolant does not leak under deformation. Because thesurfaces of the heat sink 106 may be corrugated, there may be openingsin the heat sink 106 that the elastomer 110 should block. The elastomerlayer 110 could also be replaced with an array of springs which providea large number of distributed load points across the top of the PFC orLPFC heat sink 106.

Referring now to FIG. 2, a detailed view of a portion of the coolingdevice 106 is shown in cross-section. This view shows an LPFC embodimentthat has corrugated plates 202 connected by stacked pin slices 204. Theindividual slices 204 are laterally linked to one another by flexibleconnecting elements 206. The corrugated lids 202 allow relative verticaldisplacement of the stacks of pin slices 204 as well as lateraldisplacement. The connecting elements 206 are curved and flexible,allowing compression and extension between pin stacks 204 during lateraldisplacement. In the case of a PFC heat sink, the connecting elements206 may be omitted. In any case, connecting elements 206 located invertically neighboring layers should not be bonded to one another tomaintain flexibility. As such, a gap is visible in FIG. 2 between theconnecting elements 206 of adjacent levels. This gap allows coolant flowthrough the heat sink 106 as well.

It is specifically contemplated that the pin slices 204 may be formedfrom copper or a copper alloy, but it should be understood that anymaterial with good heat conducting properties may be used instead. It isfurther contemplated that the connecting elements 206 may be formed fromthe same material as the pin slices 204 and that the slices 204 and theconnecting elements 206 may be formed by etching sheets of material. Thelayers may also be formed using punch dies, by electroplating on apattern, or by any other appropriate fabrication method. The individuallayers may be simply arranged above one another, or the layers may havean adhesive or other type of bond between the slices 204. Bonding theslices 204 provides strength and improves heat conduction betweenadjacent slices 204, but may decrease flexibility in some cases.

Referring now to FIG. 3, a top-down view of a layer of pin slices 204 isshown. The layer is formed from pin slices 204, connected by connectinglinks 206. As shown, the connecting links 206 are curved to allowflexibility. The flexibility of the connections between laterallyadjacent stacks of pin slices 204 may be increased by removing orthinning the links 206 using, for example, an etching process or amechanical separation with an edged die. This allows precise control ofthe structure of the layers with respect to the connections betweenslices 204.

Although the links 206 are shown as being arranged in a regular pattern,the flow rate of coolant through the device 106 may also be controlledby selectively adding or removing links. Additionally, the links in inadjacent layers may be arranged to match or differ in the direction oftheir curve. For example, a stack of links that curve in the samedirection will limit coolant flow more than if those links alternate incurve direction, allowing wider gaps between them. Links near the edgeof the cooling device 106 that connect the same pair of slices 204 inadjacent layers serve to reduce flow in an inactive area of the chip104. To allow flow to an area, the links may be arranged to curve indifferent directions, to connect to different slices 204, or to beentirely absent in an area of high flow—bearing in mind that each slice204 may be connected to at least one neighboring slice 204 to maintainstructural integrity. In this manner, the cooling device 106 may bedesigned to have a three-dimensional network of connections 206, thedensity of which along any given plane optimizes coolant flow around thechip, providing additional flow to areas that need additional coolingand reducing flow to areas that need less.

The use of curved links 206 provides additional options for customizingthe rate of cooling. For example, consider two stacked layers. If twoadjacent pin slices 204 in a given layer are connected by a link 206that curves in a first direction, the corresponding pin slices 204 inthe adjacent layer may be connected by a link 206 that curves in asecond direction. This allows more coolant flow than two stacked links206 that curve in the same direction. Additionally, although links 206are shown using a single, uniform curvature, the shapes of the links 206may be varied and may be non-uniform. For example, links in areas wherehigh flexibility is needed may have multiple curves or may have curvesthat are more pronounced, allowing for additional lateral motion of thecooling device 106. Links 206 in areas where less flexibility is neededor desired may have shapes that are less flexible, lending additionalstrength to the cooling device 106. The links 206 are essentiallysprings, and the spring constant of each link 206 may be controlled asappropriate.

Referring now to FIG. 4, a three-dimensional view of a “top” of oneembodiment for the lids 202 of the cooling device 106 is shown. The lid202 includes a set of pin contacts 402 that align with the pin slices204 of the adjacent layer. The pin contacts 402 are flexibly connectedto a lid body 404. As shown, gaps between the pin contacts 402 and thelid body 404 provide flexibility that allows the lid contacts 402 toshift laterally with respect to one another, as well as transversely tothe body 404.

Referring now to FIG. 5, a three-dimensional view of a “bottom” of thelids 202 of the cooling device 106 is shown. From this angle, a set ofcylindrical protrusions 502 are visible which are shown in cutaway toreveal a flexible ring 504 around the pin contacts 402. It isspecifically contemplated that the lids will be made of copper, with thepictured structures created by an etching process, but it should beunderstood that the described embodiments may be formed using anyappropriately conductive and flexible material and by any appropriateprocess, including, e.g., stamping and molding.

These embodiments of the lids 202 allow the individual pins to movevertically to conform to local deviations on the chip 104, but they alsoallow larger-scale deviations, such that the entire lid may flex toconform to a curved surface. In this manner, the PFC cooling device 106may be used to provide cooling to a wide variety of surfaces that werenot previously feasible. Although only two examples are shown herein, itis contemplated that those having ordinary skill in the art would beable to apply the present principles to create other shapes ofcorrugated lid in accordance with the present principles.

In one exemplary embodiment, the thickness of the lids is about 0.25 mm,with pin spacing in the range of 1.0 mm. These dimensions can be scaledup or down depending on the coolant type and the device to be cooled.These dimensions are provided for typical scenarios using semiconductordevices and liquid coolant, but for example a coolant having a lowerviscosity (such as air) could have a smaller pin spacing withoutsacrificing coolant flow. It is similarly contemplated that pindiameters may be about 0.5 mm. Pin diameter for a given pin spacingtrades off thermal effectiveness with coolant pressure drop, as largerpins have a higher surface area but block more of the coolant flow.

In an alternative embodiment of a corrugated lid, a complete orpartially complete stack of layers 204, including the top and/or bottomlid 202, may be pressed together. This creates a ‘u’-shaped connectionbetween neighboring pins, rather than the flat connection created by aflat plate, as the once-flat membrane/plate is forced inward between thepins.

Referring now to FIG. 6, a method of applying a cooling device to asurface is shown. Block 602 places a PFC or LPFC cooling device 106 ontoa curved surface. In the present embodiments, the surface may includechip 104 or any other curved surface that needs cooling. It should berecognized that the “curved surface” discussed herein need not have asmooth curve, but may have a stepped contour or any arbitrary shape.After the cooling device 106 is placed on the curved surface, block 604applies a load 112 to the cooling device 106 that causes it to conformto the contours of the surface. To accomplish this, the load 112 itselfshould have some ability to conform to the contours as well, or shoulduse an elastic or compressible layer 110 (e.g., an elastomer ordistributed spring) to translate the flat force of the load 112 to thecurved contour of the top surface of the cooling device 106. Block 606then causes the cooling device 106 to conform to the curved surface,where the corrugated lids 202 and the curved links 206 allow bothvertical displacement as well as lateral displacement.

Referring now to FIG. 7, an embodiment is shown with a LPFC heatsinkbeing applied to a curved surface 104. The corrugated plates shiftvertically as well as horizontally with respect to one another, allowingthem to accommodate the overall curve of the surface 104. In particular,the pins 702 in the center are relatively parallel with respect to oneanother, being over a flat portion of the surface 702, while the pins704 at the ends are tilted to accommodate the curve. Also shown is theelastic layer 706, which conforms to the top surface of the topcorrugated plate as a down pressure is applied. The elastic propertiesof the layer 706 help to distribute the downward force across the curvedsurface, which a rigid load would be unable to do. While less force willbe applied to the outer pins 704 than to the inner pins 702, thecorrugated configuration of the plates allows the entire heatsink toassume the shape of the surface 104 with less extreme pressures.

While the curved surface 104 is shown as having a relatively uniformshape, it should be understood that the surface 104 can have any shape.In particular, it should be recognized that the surface 104 can havelocal irregularities as well as global curvature, and that the pins willaccommodate these irregularities primarily with vertical displacement.

Referring now to FIG. 8, an illustration of a curved surface 802 with alocal irregularity is shown. In this instance, a single pin 804displaces vertically to accommodate the irregularity in the surface 802.As above, the elastic layer 706 conforms to the top surface of thecorrugated plate to provide downward pressure on the displaced pin 804as well as on the remainder of the plate, thereby providing good thermalcontact for the entire heat sink. While the figure shows a sectionmoving in its entirety, it should be noted that both the top and bottomplates are essentially contiguous, forming a seal for the coolantflowing between them.

Thus, by providing the ability to deform vertically and horizontally,the present embodiments provide compliant heatsinks that can accommodateany surface geometry without applying a large force. This allows thepresent embodiments to be used on relatively delicate,irregularly-shaped surfaces, where a large amount of force mightotherwise damage the device to be cooled.

The flowchart and block diagrams in the Figures illustrate thefunctionality, and operation of possible implementations of systems andmethods according to various embodiments of the present invention. Itshould also be noted that, in some alternative implementations, thefunctions noted in the blocks may occur out of the order noted in thefigures. For example, two blocks shown in succession may, in fact, beexecuted substantially concurrently, or the blocks may sometimes beexecuted in the reverse order, depending upon the functionalityinvolved.

Reference in the specification to “one embodiment” or “an embodiment” ofthe present principles, as well as other variations thereof, means thata particular feature, structure, characteristic, and so forth describedin connection with the embodiment is included in at least one embodimentof the present principles. Thus, the appearances of the phrase “in oneembodiment” or “in an embodiment”, as well any other variations,appearing in various places throughout the specification are notnecessarily all referring to the same embodiment.

It is to be appreciated that the use of any of the following “/”,“and/or”, and “at least one of”, for example, in the cases of “A/B”, “Aand/or B” and “at least one of A and B”, is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This may be extended, as readily apparent by one of ordinaryskill in this and related arts, for as many items listed.

Having described preferred embodiments of a pin fin compliant heat sinkwith enhanced flexibility and methods for using the same (which areintended to be illustrative and not limiting), it is noted thatmodifications and variations can be made by persons skilled in the artin light of the above teachings. It is therefore to be understood thatchanges may be made in the particular embodiments disclosed which arewithin the scope of the invention as outlined by the appended claims.Having thus described aspects of the invention, with the details andparticularity required by the patent laws, what is claimed and desiredprotected by Letters Patent is set forth in the appended claims.

The invention claimed is:
 1. A heat sink, comprising: a top and bottomplate, at least one of which comprises a plurality of pin contactsflexibly connected to one another, wherein the plurality of pin contactshave vertical and lateral flexibility with respect to one another,wherein at least one of the top and bottom plates is a corrugated platethat includes interlocking protrusions on opposite sides of the plateand wherein the pin contacts are flexibly connected to one another bythe top and bottom plates; and a plurality of substantially verticalpins, each formed from a plurality of pin slice layers and eachcomprising a plurality of pin slices arranged vertically between the topand bottom plates such that the plurality of pin slices formsubstantially vertical pins connecting the top and bottom plates.
 2. Theheat sink of claim 1, wherein the corrugated plate includes open spacearound each of said protrusions to allow flexibility.
 3. The heat sinkof claim 1, wherein the plurality of pin slices layers each furthercomprises a plurality of curved links between pin slices.
 4. The heatsink of claim 3, wherein the curved links of adjacent pin slice layersare arranged vertically to block coolant to regions of lower coolantneeds.
 5. The heat sink of claim 3, wherein the curved links ofrespective pin slice layers are omitted to increase coolant to regionsof higher coolant needs.
 6. The heat sink of claim 1, further comprisinga compressible layer disposed over the top plate, configured todistribute a load force to the top plate when the top plate is deformed.7. The heat sink of claim 1, wherein the bottom plate is disposed on anon-flat surface and conforms to the shape of the non-flat surface underload and wherein the vertically arranged pin slice layers communicatethe shape of the non-flat surface to the top plate, which deformsvertically and laterally to conform to the non-flat surface.
 8. A linkedpin fin compliant heat sink, comprising: a top and bottom plate, eachcomprising a plurality of pin contacts, wherein at least one of the topand bottom plates is a corrugated plate that includes interlockingprotrusions on opposite sides of the plate and wherein the pin contactsare flexibly connected to one another by the top and bottom plates; aplurality of pin slice layers, each comprising a plurality of pinslices, arranged vertically between the top and bottom plates such thatthe plurality of pin slices form substantially vertical pins connectingthe top and bottom plates; and a plurality of curved links connectinglaterally adjacent pin slices in at least a pin slice layer.
 9. Thelinked pin fin compliant heat sink of claim 8, wherein the corrugatedplate includes open space around each of said protrusions to allowflexibility.
 10. The linked pin fin compliant heat sink of claim 8,wherein the curved links between vertically adjacent pin slice layersare arranged to align vertically to block coolant to regions of lowercoolant needs.
 11. The linked pin fin compliant heat sink of claim 8,wherein one or more curved links of at least a respective pin slicelayer are omitted to increase coolant to regions of higher coolantneeds.
 12. The linked pin fin compliant heat sink of claim 8, whereincurved links between corresponding pin slices on at least two adjacentlayers curve in different directions with respect to one another. 13.The linked pin fin compliant heat sink of claim 8, wherein the curvedlinks have a thinner vertical cross-section than the pin slice layers.14. The linked pin fin compliant heat sink of claim 8, wherein theplurality of curved links are arranged to create regions of highercoolant flow and regions of lower coolant flow, such that coolantthrough the heat sink follows a specified path.
 15. A heat sink,comprising: a top and bottom plate, at least one of which comprises aplurality of pin contacts flexibly connected to one another, wherein theplurality of pin contacts have vertical and lateral flexibility withrespect to one another, wherein at least one of the top and bottomplates is a corrugated plate that includes interlocking protrusions onopposite sides of the plate and wherein the pin contacts are flexiblyconnected to one another by the top and bottom plates; a plurality ofsubstantially vertical pins connecting the top and bottom plates; and acompressible layer disposed over the top plate, configured to distributea load force to the top plate when the top plate is deformed.
 16. Theheat sink of claim 15, wherein the vertical pins comprise a plurality ofpin slice layers, each comprising a plurality of pin slices, arrangedvertically between the top and bottom plates such that the plurality ofpin slices form substantially vertical pins connecting the top andbottom plates.
 17. The heat sink of claim 16, wherein the bottom plateis disposed on a non-flat surface and conforms to the shape of thenon-flat surface under load and wherein the vertically arranged pinslice layers communicate the shape of the non-flat surface to the topplate, which deforms vertically and laterally to conform to the non-flatsurface.
 18. The heat sink of claim 16, wherein the plurality of pinslices layers each further comprises a plurality of curved links betweenpin slices.
 19. The heat sink of claim 18, wherein the curved links ofadjacent pin slice layers are arranged vertically to block coolant toregions of lower coolant needs.
 20. The heat sink of claim 18, whereinthe curved links of respective pin slice layers are omitted to increasecoolant to regions of higher coolant needs.